The present invention relates to an electrical switch, and more particularly an electrical switch for power tools.
Such electrical switches are used as ON/OFF switches in power tools, such as drilling machines, angle grinders or the like. In particular, the electric tools may be those which are operated with direct current.
DE 31 26 816 C2 discloses an electrical switch for electric tools. The switch has switching contacts like a contact bridge which are arranged on a slide and also associated fixed contacts. The slide can be moved between two positions by means of a manually actuable actuator. The switching contacts are at a distance from the fixed contacts in one position, namely the OFF position, and bear against the fixed contacts in the other position, namely the ON position. An elastic means designed as a torsion spring interacts with the slide and the actuator, so that the slide can be changed over between the two positions with a type of snap movement.
During the changeover between the two positions, considerable spring energy is stored in the torsion spring, this spring energy being introduced by the manual action on the actuator until the changeover point is reached. This spring energy is then released suddenly when the changeover point is crossed in the snap movement. It has now been found that chatter between switching and fixed contacts, in particular during the changeover from the OFF position into the ON position, may occur in the process, which has an adverse effect on the service life of the switch.
The object of the invention is to further develop the switch in such a way that its service life is prolonged and that, in particular, the contact chatter of the switch is reduced.
The elastic means of the switch according to the invention is designed as a first spring like a pressure-point spring. During movement of the slide, the first spring interacts with a switching-point link for generating a pressure point. As a result, a spring force acts against the direction of movement of the slide up to the changeover point, so that the movement of the slide from the OFF position into the ON position is first of all effected with a slow action while the switching contact approaches the fixed contact. Once the changeover point has been overcome, the distance still remaining between the switching point and the fixed contact is now covered with a snap movement of the slide. Since the snap movement is effected only when covering this very small distance, contact chatter is largely ruled out. Further refinements of the invention are described below.
It is especially preferred to design the elastic means as a combination of the first spring and a further second spring located on the slide. During movement of the slide, the second spring produces a further spring force, the further spring force acting against the direction of movement of the slide up to the changeover point and in the direction of movement of the slide when the changeover point has been overcome, so that the second spring therefore has an assisting action during the snap movement of the slide. During the changeover from the ON position into the OFF position, the slide first of all remains stationary, and thus the switching contact remains bearing against the fixed contact until the changeover point is reached. When the changeover point has been overcome, an abrupt separation of the switching contact from the fixed contact is then effected by the snap movement of the slide, so that arcs which may possibly occur are immediately extinguished. Destruction of the contacts, in particular in direct-current operation, is thus effectively countered.
The second spring may be designed as a compression spring. During the movement of the slide from the one position, this compression spring is loaded during the generation of the pressure point until the changeover point is reached, so that a resetting force acts against the direction of movement of the slide. When the changeover point is overcome, the compression spring then relaxes, in the course of which a force acts in the direction of movement of the slide.
The manual actuation is transmitted from the actuator to the contact system by means of a sliding member for example. To this end, the sliding member, by acting on the second spring, is in operative connection both with the slide and with the actuator. The sliding member is arranged so as to be movable in a guide on the slide. Two extensions assigned to the slide are located on the sliding member, in which case, on the one hand, the extensions interact with the guide and, on the other hand, in each case one extension acts on one end of the second spring.
In a further refinement, a receptacle like a rectangular chamber for the second spring is located on the slide. The guide for the sliding member adjoins the receptacle on both sides. The receptacle has openings relative to the guide on these two sides in such a way that the respective extension located on the sliding member can be guided into the receptacle for acting on the associated end of the second spring.
Furthermore, in each case a stop may be arranged at the extension on the sliding member, this stop interacting with a corresponding stop on the receptacle, for example with the chamber wall located at the transition between the guide and the receptacle. There is preferably clearance of motion between the two corresponding stops, such that, when the sliding member is actuated, first of all the second spring is acted upon, and the slide can be moved from the one position in the direction of the other position by means of the associated corresponding stops after the clearance of motion has been overcome. This clearance of motion assists the sequence of movement during the changeover, in particular with regard to the snap movement and the abrupt contact separation during the changeover from the ON position into the OFF position.
In a further refinement, the first spring is designed as a leaf spring with an elastic leg. The leaf spring is arranged approximately parallel to the plane of motion of the slide. An approximately V-shaped lug is located at the end of the elastic leg, the V-shaped lug interacting with a corresponding extension of the switching-point link, the extension being located on an inner wall of the housing for the switch. The leaf spring is expediently designed in a bow shape with two elastic legs like a U. A holder for the leaf spring is arranged on the slide, the holder being located on that end of a part of the guide which is opposite the receptacle. The base of the U-shaped leaf spring can thus be inserted into the holder for fastening.
Finally, a further third spring, which is designed as a compression spring, may be arranged on the sliding member. One end of the third spring bears against a stop fixed to the sliding member and the other end of the third spring bears against a stop fixed to the housing. As a result, a resetting force comes into effect when the sliding member is actuated, this resetting force at the same time serving to reset the actuator as soon as the manual action on the actuator has ended. A type of rectangular chamber may be located on the sliding member for accommodating the third spring. It is then advisable for the stop fixed to the sliding member to be formed by a wall of the chamber, whereas the stop fixed to the housing projects into the chamber.
The switching contact itself is likewise provided with a compression spring, so that the switching contact can be brought to bear against the fixed contact by means of spring pressure in the ON position. In this case, the first and second springs are located on one side of the slide, whereas the switching contact is arranged on the other, opposite side of the slide. In particular, the first and second springs are located on that side of the slide which faces the sliding member, and the switching contact with its compression spring is located on that side of the slide which is facing away from the sliding member.
The first spring should expediently have such a spring constant that the spring force of the first spring exerted at the changeover point is at least as great as the sum of the spring forces which are exerted by the compression springs at all the switching contacts. This ensures immediate contact separation at the changeover point during the changeover from the ON position into the OFF position. Furthermore, it is expedient for the extension of the switching-point link to be of asymmetrical design with flanks having different slopes. In this case, the steeper flank faces the OFF position and the gentler flank faces the ON position. This ensures, on the one hand, that the slow-action contact approach already mentioned until the changeover point is reached is effected during the changeover from the OFF position into the ON position. On the other hand, it is also ensured that, in interaction with the force of the compression spring at the switching contact, a contact separation during the changeover from the ON position into the OFF position is ruled out before the changeover point is reached.
The advantages achieved with the invention consist in particular in the fact that chatter of the contacts during the switching from the OFF position into the ON position is largely avoided. When switching back from the ON position into the OFF position, rapid, sudden opening of the contacts is achieved, which reduces the contact erosion. The service life of the contacts is therefore prolonged compared with previous switches.
In particular during use of the switch for switching direct current, any arcs which occur are immediately extinguished. Destruction of the contacts by arc action is therefore effectively prevented. The switch according to the invention is therefore also suitable for large switching capacities.
The movable parts of the switch have less friction than hitherto. As a result, the wear is lower and the service life of the switch is further increased.
The switch according to the invention also advantageously has smaller hysteresis between the ON position and the OFF position than previous switches. As a result, the user senses the switching more uniformly.
Furthermore, the switch has a small number of parts, these parts being simple and cost-effective. In addition, the switch is simple to mount. The switch according to the invention can thus be manufactured in a cost-effective manner.